Electrical printing using plural electrical fields with single powder bed



3,461,795 LDS wrra Aug. 19, 1969 A. s. DECKER ET AL ELECTRICAL PRINTING USING PLURAL ELECTRICAL FIE SINGLE POWDER BED 5 Sheets-Sheet 1 Filed May 4, 1967 INVENTCRS Aug. 19, 1969 A. s. DECKER ETAL 3.461,795

ELECTRICAL PRINTING USING PLURAL ELECTRICAL FIELDS WITH SINGLE POWDER BED Filed May 4, 1967 1 I 5 Sheets-Sheet? A k g m O 3 N N s, N w w Aug. 19, 1969 ELECTRICAL PRINTING Filed May 4, 1967 A. s, DECKER ET AL USING PLURAL ELECTRICAL FIELDS WITH SINGLE POWDER BED 5 Sheets-Sheet 5 Aug. 19, 1969 A. s. DECKER ETAL 3,461,795

ELECTRICAL PRINTING usmc PL L ELECTRICAL FIELDS WITH 1 SINGLE PO D 5 Sheets-Sheet 4 R BE Filed May 4. 1967 INVENTOR-S fizz-429 pay/5e BY/ /f ,i Mpamu/ 3,461,795 LDS Wm:

' Ati-g. 19, 1969 A. s. DECKER ET AL ELECTRICAL PRINTING USING PLURAL ELECTRICAL FIE swam POWDER BED I 5 Sheets-Sheet 5 Filed May 4, 1967 United States Patent 3,461,795 ELECTRICAL PRINTING USING PLURAL ELEC- TRICAL FIELDS WITH SINGLE POWDER BED Alfred S. Decker and Luther H. Wideman, Toledo,

Ohio, assignors to Owens-Illinois, Inc., a corporation of Ohio Filed May 4, 1967, Ser. No. 636,047 Int. Cl. B41f 17/08, /00; B411 31 /00 U.S. Cl. 101--40 9 Claims ABSTRACT OF THE DISCLOSURE Cross references to related applications The present invention employs two or more offset plate conveyors of the type disclosed and described in detail in a co-pending application of A. S. Decker et al., Ser. No. 615,206, filed Feb. 10, 1967, now Patent No. 3,357,349, assigned to the assignee of the present application. The techniques disclosed in the co-pending application of William E. Johnson, Ser. No. 439,799, filed Mar. 15, 1965, now Patent Number 3,301,179, assigned to the assignee of the present application are employed to independently control the individual electric fields associated with each of a plurality of stencil screens. The offset plate assemblies upon the offset plate conveyors have the image applied to them in accordance with the present invention and the image is subsequently electrostatically transferred from plate assemblies to articles in the form of bottles carried on a bottle conveyor, the copending application of A. S. Decker, et al., Ser. No. 595,490, filed Nov. 18, 1966, now Patent No. 3,387,557 assigned to the assignee of the present application disclosing details of the transfer of the image from the offset plate to the bottle. 1

Background of the invention The present invention is concerned with electrostatic printing processes of the type wherein printing powder particles are electrically impeled from a supply bed through the aperture of a stencil screen to a substrate surface. The above-mentioned Johnson Patent No. 3,301,179 discloses an electrostatic printing process of this type, and further discusses and proposes a solution for problems arising in those cases where successive images are transferred from a supply bed without replenishing or reconditioning the bed between successive transfers. In brief, an electrically conductive stencil screen having an image aperture is located in spaced overlying relationship with a bed of printing powder particles. The substrate surface to be printed is then brought into spaced vertical registry above the stencil screen and an electric field is established which extends from beneath the bed, usually in the form of a conductive plate supporting the bed, to the substrate surface. The powder particles within the bed are electrically charged and impeled by the field through the apertures to the substrate surface. It has been found that successive transfers of images from the bed causes a packing of the bed which makes it successively more diflicult to impel particles from the bed. In the Johnson Patent No. 3,301,179, this problem is over- 3,461,795 Patented Aug. 19, 1969 ice come by measuring the accumulation of charged particles on the substrate surface and continuing the application of the electric field until a predetermined quantity of particles has accumulated on the substrate surface.

In the co-pending Decker, et a1. Patent No. 3,357,349, there is disclosed a powder supply arrangement in which an elongate powder bed is reciprocated beneath the stencil screen so that a fresh powder surface is more or less continuously moved into vertical registry with the screen. At the end of each reciprocating stroke, a charge of powder is dropped onto the bed at a location such that it will be conveyed beneath the stencil screen on the next subsequent stroke of the bed. A doctor mechanism between the location at which the charge is deposited and the stencil screen smooths the bed out as the bed is moved.

In the present invention, the techniques of the Johnson Patent No. 3,301,179 and the Decker, et al. Patent No. 3,357,349 are combined into an arrangement such that the powder bed of the Decker, et al. Patent No. 3,357,349 may be employed to simultaneously service two or more stencil screens located above the path of travel of the bed so that the production rate of the printing apparatus can be correspondingly increased.

Summary By the use of the present invention, a plurality of powder images may be simultaneously electrostatically transferred from a common supply bed through a plurality of stencil screens to each of a plurality of individual substrate surfaces. This is accomplished by establishing an individual electric field for each stencil-substrate unit and by further independently regulating the time duration of application of each individual electric field so that images of uniform density on each of the substrates are obtained, even though the condition of the powder supply bed may vary beneath the different stencil screens.

In the drawings:

FIGURE 1 is a side elevational view, with certain parts broken away or omitted, of an electrostatic printing apparatus embodying the present invention;

FIGURE 2 is a top plan view of a portion of the apparatus of FIGURE 1, again with certain parts broken away or omitted;

FIGURE 3 is an end elevational view of the apparatus of FIGURE 1, with certain parts broken away;

FIGURE 4 is a detail cross sectional view taken approximately on line 4-4 of FIGURE 2; and

FIGURE 5 is a detail cross sectional view taken approximately on the line 55 of FIGURE 4.

Referring first to FIGURES 1 through 3, an electrostatic printing apparatus embodying the present invention includes a pair of like offset plate conveyors designated generally 20A and 20B mounted in parallel side-'by-side relationship to each other and in operative relationship with a bottle conveyor designated generally 22. A printing powder supply mechanism designated generally 24 which includes powder dispensing hoppers 26A and 26B is located in operative relationship with plate conveyors 20A and 20B.

Each of offset plate conveyors 20A and 20B are the same as the offset plate conveyor disclosed and described in detail in the above-mentioned co-pending A. S. Decker, et al., Patent No. 3,387,557 and bottle conveyor 22 is likewise described in that application. A powder supply system adapted for operation with a single offset plate conveyor is disclosed and described in detail in the aforementioned co-pending A. S. Decker, et al. Patent No. 3,357,349. The powder supply hoppers of the Decker et a1. Patent No. 3,357,349 are controlled and actuated in the same manner as are the hoppers 26A and 26B of the present application. The present application is especially directed to modifications in the powder supply bed arrangement which permit simultaneous operation of two or more offset plate conveyors in conjunction with a common powder supply bed. While the present application discloses the invention as applied to an apparatus having two offset plate conveyors, it will be apparent from the following description that the system is equally well adapted for use with more than two offset plate conveyors.

To briefly summarize the operation of plate conveyors A and 20B, the conveyors are driven in step-by-step movement so that each of the individual offset plate as semblies 28 are advanced to the position previously occupied by the preceding plate assembly. Referring to FIGURE 1, the offset plate assemblies 28 are sequentially advanced to a decorating position in adjacent registry with the path of movement of articles in the form of bottles B on conveyor 22. As described in detail in the aforementioned Decker, et al. Patent No. 3,387,557, the plate assemblies are so constructed that when at the decorating position, the plate assembly can be horizontally projected to the right as viewed in FIGURE 1 into contact with the bottle, the projecting mechanism including a cam assembly designated generally 30. Bottle conveyor 22 is driven in continuous movement at a rate synchronized with the plate conveyors 20A and .203 so that as the plate 28 is projected into the path of movement of the bottle, a bottle B on conveyor 22 is conveyed past the plate, the bottle rolling along the surface of the plate. Freely rotatable chucks 32 and 34 on the bottle conveyor permit the rolling movement of the bottle. In the Decker, et al. Patent No. 3,387,557, a single offset plate conveyor was employed, while in the present case two plate conveyors 20A and 20B are employed. This permits bottle conveyor 22 to be actuated at twice the speed of that in Decker, et al. Patent No. 3,387,557.

At the end of each step of movement of the conveyors 20A and 20B, an offset plate assembly 28 is located at a printing station in registry with a stencil screen 36, as best seen in FIGURES 4 and 5. Preferably, at the printing station, the plate assembly is also projected downwardly from its normal path of movement into adjacent registry with the stencil screen as indicated by the broken line showing in FIGURES 4 and 5. The mechanism for performing this may be similar to that employed in the Decker et al. Patent No. 3,387,557 for projecting the plate assembly outwardly at the decorating position. By the application of an electric field, powder from a powder supply bed PB is electrostatically transferred through the image aperture of stencil screen 36 to the offset plate assembly, the images being represented by X in FIGURE 2. Upon subsequent arrival of the plate assembly at the decorating position with the powder image thereon, the image is electrostatically transferred from the plate assembly to the surface of the bottle while the bottle rolls laterally across the powder image on the plate assembly.

As best seen in FIGURES 4 and 5, the powder bed PB is maintained in an elongate tray designated generally 38. As described in detail in the co-pending Decker, et al. Patent No. 3,357,349, the tray 38 is driven in longitudinal reciprocatory movement beneath the two stencil screens. At the end of each stroke of movement of the tray, the tray actuates a dispensing mechanism on the hopper 26A or 263, depending on whether the tray is at its extreme left-hand or right-hand end of movement. Actuation of the dispensing mechanism by the arrival of the tray at one end limit of movement permits the hopper whose dispensing mechanism is actuated to drop a measured charge of powder upon the surface of the tray. A doctor mechanism, shown and described in detail in the Decker, et al. Patent No. 3,357,349 smooths the deposited pile of powder during the subsequent movement of the tray away from that end limit of movement.

The length of the stroke of the tray and its dimensions are such that powder in supply bed PB is located beneath both of hoppers 26A or 26B at all times. In other words,

4 referring to FIGURE 3, the tray 38, which is enclosed in housing 40, will move to the right as viewed in FIG- URE 3 until its left-hand end is approximately below hopper 26B, when the tray reaches its extreme right-hand end limit of movement. At this time, the dispensing mechanism of hopper 26A will be actuated to drop a charge of powder upon the tray. The doctor mechanism which is associated with hopper 26A is located between the hopper and conveyor 20A. Upon subsequent movement of the tray to the left as viewed in FIGURE 3, the doctor mechanism smooths the deposited charge of powder so that a smooth surface is advanced into operative registry with the plate assemblies of conveyor 20A. The amount of powder in the deposited charge is selected to be sufficient to replace the powder transferred from the tray during the preceding stroke of movement of the tray.

As previously stated, the present invention is especially adapted to modifying the powder supply arrangement disclosed in the Decker, et al. Patent No. 3,357,349, to permit the simultaneous application of images to two or more substrate surfaces from a common powder supply bed. From the foregoing dscription, it is apparent that as the powder bed is shifted transversely beneath conveyors 20A and 20B, the offset plate assemblies on that conveyor which is on the down stream side with respect to the direction of movement of the bed will be exposed only to portions of the bed from which images have been previously transferred during the passage of the bed beneath the other of the two conveyors. As described in greater detail in the aforementioned Johnson Patent No. 3,301,179, successive electrostatic transfers of powder from the same portion of a powder bed result in the application of images of varying density, the density in general decreasing as the number of successive transferred images increases. The primary reason for this effect can most simply be considered as being due to a packing effect on the powder within the bed caused by each successive transfer which makes it increasingly more difficult to impel particles from the bed through the stencil to the substrate surface.

In the Johnson Patent No. 3,301,179, a technique for achieving images of uniform density over successive transfers from the same powder bed is disclosed. The uniform density is achieved by electrically measuring the accumulation of charged particles on the substrate surface and regulating the time duration of the application of the electric field until a predetermined charge representative of the accumulation of the desired amount of powder particles on the substrate surface is measured.

In order to employ the technique described in the Johnson Patent No. 3,301,179, to the present invention, the powder bed support tray 38 is constructed with a bottom 42 and side walls 44 of electrical insulating material. The tray 38 is further supported upon its carriage 46 by a block of insulating material 48, the carriage being supported by rollers 50 which ride in ways 52 fixed to the casing 40. As described in more detail in the Decker, et al. Patent No. 3,357,349, the tray assembly is driven in longitudinal reciprocating movement by a rack 54 and pinion 56 arrangement, best shown in FIGURE 4.

At uniformly spaced intervals on the bottom 42 of the tray, a series of electrically conductive strips 58 are fixedly mounted to extend transversely across the bottom of the tray. Each strip 58 is mechanically and electrically connected to a spring loaded pin assembly 60 which projects downwardly through the bottom of the tray. Blocks of electrical insulating material 62 are mounted upon the stationary ways 52 to support in turn an' electrically conductive cam strip 64. Two cam strips 64 are employed, one being located beneath each stencil screen 36 and, as best seen in FIGURE 5, being generally co-extensive with the dimension of the stencil screen longitudinally of tray 38.

As best seen in FIGURE 5, the cam strips 64 are located to contact the pins 60 of those groups of the strips 58 which are in vertical registry beneath each stencil screen 36. Those strips 58 which are electrically connected by their pin assemblies 60 to the cam strip 64 cooperatively define one equipotential surface of the electric field employed to electrostatically transfer particles from powder bed PB to the substrate surface on offset plate assemblies 28. This arrangement affords a means for establishing independent electric fields between the powder bed and each of the two offset pl-ate assemblies. The electrical insulating properties of the powder employed are such that those strips 58 in registry with the offset plate assembly on conveyor 20B are effectively electrically insulated from the corresponding strips 58 in registry with the offset plate assembly on conveyor 20A. Because the two electric fields are thus electrically independent of each other, the field at each printing station may be independently controlled.

The electrical arrangement for electrostatically transferring powder from bed PB through the respective stencil screens 36 onto the registered offset plate assemblies 28 is shown schematically in FIGURE 5, details of the electrical system being described in the aforementioned Johnson Patent No. 3,301,179. Two similar, but electrically independent electrical systems are employed, each including voltage sources V1 and V2 respectively connected between the stencil screen 36 and cam plate 64 and between stencil screen 36 and offset plate assembly 28. The electrical connection between voltage source V2 and plate assembly 28 may be made by an electrical contact 66 carried on the offset plate assembly 28 which, when the assembly is in its final registered position with the stencil screen engages a second contact 68 mounted upon a stationary portion of the offset plate conveyor. The vertical movement of offset plate assembly 28 into and out of operative registry with the stencil screen may be employed to move the two contacts into engagement with each other. A schematic representation of the two contacts is shown in FIGURE 5, structural details of such an arrangement being disclosed in the co-pending Decker, et al. Patent No. 3,387,557.

An electrical circuit indicated schematically at 70 is connected into the electrical system to measure the accumulation of charged particles on the offset plate assembly during the electrostatic transfer of powder from the powder bed PB through stencil screen 36 to the registered offset plate assembly. As described in detail in the copending I ohnson Patent No. 3,301,179, when a predetermined number of powder particles have been accumulated upon the offset plate assembly, the circuit 70 is triggered and, acting through a suitable shut-off device 72 automatically de-energizes voltage sources V1 and V2 to shut off the electric field and thus stop further transfer of powder from the bed to the oifset plate assembly. As described in detail in the co-pending Johnson Patent No. 3,301,179, the accumulation of particles upon the offset plate assembly is measured by making the sensing circuit 70 responsive to the electric charge transferred to the offset plate assembly by the charged powder particles.

By the foregoing arrangement, the time duration of application of the electric fields can be independently controlled so that the density of the image applied to the offset plates at the respective printing stations is uniform. Thus, assuming powder bed PB to be moving to the right as viewed in FIGURE 5, the offset plate assemblies on conveyor 20B will be exposed to a portion of the bed which is relatively fresh and undisturbed, while the offset plate assemblies on conveyor 20A will be exposed to a portion of the bed which is packed since the bed must pass beneath conveyor 20B before it reaches conveyor 20A. With the independent control of the time duration of the electric fields, the electric field employed in conjunction with conveyor 20A will normally be applied for a somewhat longer period of time than will the field employed in conjunction with conveyor 20B, the longer time required by virtue of the fact that the field employed with conveyor 20A must operate on a portion of the powder bed which is somewhat packed.

In actual practice, the speed at which powder bed PB is driven may be chosen to be so low that the portions of the bed from which images are successively transferred may overlap with each other. In view of the fact that the time duration of application of the electric field during transfer will normally be between and 300 milliseconds, the' fact that the powder bed is moving during the actual transfer operation at a relatively low speed does not have any effect on the resultant image.

While the invention has been described in terms of an offset decorating operation, it is believed apparent that the same techniques are equally applicable in printing directly upon an article surface or final substrate. Thus, the surface to which the image is applied is referred to in the claims as an image receiving surface.

While one embodiment of the invention has been described in detail, it will be apparent to those skilled in the art that the disclosed embodiment may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting, and the true scope of the invention is that defined in the following claims.

We claim:

1. In an electrostatic printing process; the method of simultaneously applying powder images to each of a plurality of image receiving surfaces comprising the steps of locating a plurality of stencil screens each having an image-defining aperture therethrough in spaced side-byside relationship to each other to establish a row of sideby-side printing stations, moving an elongate supply bed of powder particles along said row of printing stations in underlying relationship to all of said stencil screens and in overlying relationship to a plurality of spaced stationary electrodes each underlying one of said screens, registering image receiving surfaces to be printed in overlying relationship to each of the respective stencil screens at each printing station, and simultaneously establishing individual electrically independent electric fields at each printing station between each of said image receiving surfaces and a localized region of said supply bed by electrically connecting each electrode to only that portion of the bed in vertical registry therewith to electrically charge and impel powder particles from those regions only of the bed in registry with the stencil screen and associated electrode through the aperture of the associated stencil screen to the registered image receiving surface.

2. In the process defined in claim 1', the step of independently regulating the application of each of said individual electric fields to achieve uniform density of all of the simultaneously applied images.

3. In the process defined in claim 1; the step of longitudinally reciprocating the supply bed beneatli said stencil screens in reciprocatory strokes having an amplitude at least equal to the distance between the outer sides of the two outermost stencil screens, and replenishing and reconditioning the bed at the end of each reciprocatory stroke.

4. In the process defined in claim 3; the step of independently regulating the application of each of said individual electric fields to achieve uniform density of all of the simultaneously applied images.

5. Electrostatic printing apparatus for simultaneously applying a powder image to a plurality of image receiving surfaces comprising a frame, a plurality of stencil screens mounted on said frame in spaced aligned sideby-side relationship to each other, a plurality of image receiving surface conveyors, one of said conveyors being associated with each of said stencil screens and operable to convey image receiving surfaces in succession into overlying vertical registry with the stencil screen, an elongate powder supply bed tray of electrically insulating material extending horizontally beneath all of said stencil screens in underlying vertical registry therewith, said tray containing and supporting a bed of printing powder particles common to all of said stencil screens, means for applying a plurality of individual electric fields comprising a plurality of electric contact means carried on said tray and in contact with said bed of powder particles at longitudinally spaced intervals on the tray, a stationary electrode coextensive with each of said stencil screens in vertically registered underlying relationship thereto beneath said tray and engageable with those contact means on said tray in vertical registry with the electrode, and independently regulated electrical circuit means connected between each electrode and its corresponding screen for applying said individual electric field to individually decorate the respective image receiving surfaces in registry with the respective screens.

6. Apparatus as defined in claim wherein said stencil screens are aligned in a row and the longitudinal extent of said tray is substantailly greater than the length of said row, means for driving said tray longitudinally in reciprocatory strokes of a length such that said bed is always located in underlying relationship with all of said stencil screens, and means operable at the end of each stroke of movement of said tray for replenishing and reconditioning the powder supply bed.

7. Apparatus as defined in claim 5 wherein said means for applying a plurality of electric fields comprising means in each of said circuit means for measuring the accumulation of charged particles upon the registered image receiving surface, and means responsive to the accumulation of a charge on the image receiving surface representative of a selected minimum quantity of particles for terminating the application of the electric field.

8. Apparatus as defined in claim 5 wherein said tray comprises a bottom and side members of electrical insulating material, said contact means comprises a plurality of spaced strips of electrically conductive material mounted upon and extending transversely across the bottom of said tray in contact with the powder, and means for electrically connecting those strips only on said tray which are located in overlying relationship to one of said electrodes.

9. Apparatus as defined in claim 8 wherein said means for connecting said strips to an electrode comprises a spring-loaded pin electrically connected to each strip and projecting downwardly through and below the bottom of said tray, each of said electrodes comprising an electrically conductive cam strip mounted upon said frame in underlying relationship beneath each of said stencil screens to engage the pins connected to the strips underlying the respective stencil screens.

References Cited UNITED STATES PATENTS 3,301,179 1/1967 Johnson 101l 14 3,342,126 9/1967 Nesin et al. 10l90 3,357,349 12/1967 Decker et al. 101-129 XR EDGAR S. BURR, Primary Examiner US. Cl. X.R. 

